IMPROVEMENTS IN AND RELATING TO DRIVE MECHANISMS SUITABLE FOR USE IN DRUG DELIVERY DEVICES

摘要

The invention relates to a drive mechanism for use in a drug delivery device comprising: a housing (2); a dose dial sleeve (40) having a helical thread of a first lead; and a two-part piston rod (14). The said two-part piston rod (14) comprises an outer part (18) having a helical thread of a second lead and an inner part (16) having a helical thread of a third lead, whereby the first lead of the thread of the dose dial sleeve (40) is equal to the sum of the second lead of the thread of the outer part (18) of the piston rod (14) and the third lead of the thread of the inner part (16) of the piston rod (14).